In one form of a fluid control valve, a flow control element is movably positioned in a valve chamber to open or close the valve. The flow control element may be directly actuated by a solenoid operated plunger operatively associated with the flow control element. The solenoid coil controllably positions the plunger to move the flow control element to an actuated position. To avoid a requirement for high powered solenoids, certain flow control valves further include a pilot valve operatively disposed between the plunger and the flow control element. The pilot valve must overcome lesser hydraulic forces, thus requiring a lower power solenoid.
With a unidirectional valve, the flow control valve operates correctly if fluid flow is in only a single direction, i.e., from an inlet port to an outlet port. In certain applications it is desirable to use a bidirectional valve to control fluid flow in either direction. Bidirectional valves incorporating a Wheatstone bridge concept provide suitable control.
One known bidirectional control valve uses a flow control element including four internal passages each having a check valve. European Patent No. 0 204 666 discloses such a valve. A common passage connects two unloading passages to provide a pilot opening opened or blocked by a solenoid operated needle. Such a structure requires that the solenoid operated needle have sufficient stroke to permit sufficient movement of a plunger. This requires a higher power solenoid.
Carbon U.S. Pat. No. 2,480,712 discloses a bidirectional fluid flow control valve that uses a pilot valve having a pilot chamber separate from a valve chamber. Such a valve cannot fit into existing or standard cavities such as in a manifold.
The present invention overcomes one or more of the problems discussed above.